All communications using non-return-to-zero (NRZ) or frequency modulated carrier waves are susceptible to noise. However, NRZ offers many advantages, such as predictable power consumption and good range and penetration characteristics. Thus, NRZ carrier waves are often used for communications.
When a NRZ carrier wave is involved in communications on a printed circuit board and with semiconductor devices (integrated circuits), various techniques may be used to reduce noise. Often, the communications signal is transmitted as a differential signal, across two matched traces on the printed circuit board. The two matched traces each carry a signal which can be divided into two parts. Of the two parts, the differential part of the signal is what is desired and the common mode part of the signal is what is not desired.
Unfortunately, this requires that the integrated circuits reduce common mode noise received or sent along differential pairs of traces. Many integrated circuits are not effective enough at this task (reduction of common mode noise) to operate as well as desired. Moreover, constraints on the design of printed circuit boards may increase common mode noise. For example, a bend in a pair of differential traces may cause differential mode energy to be converted to common mode energy, and thus increase the common mode energy (or noise).
Other embodiments within the spirit and scope of the present invention will be apparent from the description and drawings.